Liquid crystal displays are display panels that control transmission/blocking of light (ON/OFF of display) by controlling the alignment of birefringent liquid crystal molecules. Methods for aligning liquid crystal molecules include a rubbing method in which certain treads are formed on an alignment film material applied by a roller or the like so that an alignment film is formed.
Alternatively, as in the multi-domain vertical alignment (MVA) mode, the alignment of liquid crystal molecules may be controlled by means of alignment control structures such as bank-like protrusions comprising a dielectric material extending in an oblique direction on a common electrode and slits formed in parallel with such bank-like protrusions on pixel electrodes, without performing any alignment treatment (see Patent Document 1).
In a liquid crystal display device in the MVA mode, liquid crystal molecules are aligned vertically to a substrate face when a voltage is not applied. When a voltage is applied between a pixel electrode and a common electrode, liquid crystal molecules are aligned at an angle corresponding to the applied voltage. At this time, slits or bank-like protrusions provided in the pixel electrode form a plurality of domains in each pixel. In the domains, the tilt direction of the liquid crystal molecules varies from domain to domain. The display propertied can be enhanced by such formation of a plurality of domains, in which the tilt direction of the liquid crystal molecules varies from domain to domain in each pixel.
Here, a region where slits or protrusions are formed tends to have lower light transmittance. Simplified arrangement of these, and wider spacing between bank-like protrusions or slits of the pixel electrode improves the light transmittance. However, too-large spacing between bank-like protrusions or slits leads to a longer time required to transfer the tilt direction to all the liquid crystals. As a result, the response of liquid crystal molecules becomes poorly slow when a voltage required for display is applied to a liquid crystal layer.
As a method for counteracting such poor response, a method of forming a polymer film on an alignment film (hereinafter, also referred to as “PSA (Polymer Sustained Alignment) technology”) is employed, in which polymerizable monomers in liquid crystal materials injected between substrates are polymerized while an voltage is applied thereto so that a polymer film storing a tilt direction of liquid crystal molecules (see Patent Document 2).
Patent Document 2 also discloses a method using a monomer having one or more ring structures or ring-fused structures and two functional groups directly bonded to the ring structures or ring-fused structures, as a polymerizable monomer used in the PSA technology. Such a method is used as a means for solving image sticking which is an afterimage produced when a displayed image is changed after a long-time display of the same image in a liquid crystal display device.
Patent Document 1: JP-A 2006-189610
Patent Document 2: JP-A 2003-307720